This invention relates to improvements in boring apparatus for forming horizontal holes for pipe installation beneath roadways, sidewalks, driveways and the like and includes an improved automatically operated guiding system so that the location of the hole at the end of the bore can be accurately predicted.
In laying pipelines that traverse roadways and the like, it is a common practice to provide excavated ditches, openings or pits at opposite sides of the roadway and to tunnel between the same beneath the roadway to avoid the time and expense of digging up the roadway and replacing it as exemplified in U.S. Pat. Nos. 2,349,033, 3,132,701, 3,451,491 and 4,249,620.
In such procedure, a boring head is started in one ditch to exit in the other and there is an ever present problem of maintaining a proper plane of movement of the head through the subsoil so that it will exit at the desired location in the far ditch. Addressing this problem, U.S. Pat. No. 2,349,033 provides fixed radial fins on the trailing or force receiving end of the head calculated to maintain the boring head on a line in which it is originally started but does not provide for correction for deviation from such line. In U.S. Pat. No. 3,132,701, an hydraulic cylinder is used to raise or lower the trailing end of the head to change the pitch of the bore but this is a fixed correction which must be monitored and deliberately readjusted from time to time depending upon the actual plane of movement. U.S. Pat. No. 3,451,491 provides a guide frame which can be raised or lowered at the trailing end by a screw jack and thus has the same drawbacks as the device in U.S. Pat. No. 3,132,701. In U.S. Pat. No. 4,249,620, a small pilot hole is first formed which is later enlarged and for purpose of alignment, if it is determined that the pilot hole is not properly aligned, a new one is formed. It is apparent that these prior devices for establishing a desired path of movement of a horizontal boring head have the disadvantage of being fixed adjustments that are not responsive to any deviation from the line set and must be constantly monitored on a more or less trial and error basis for continual manual adjustment and resetting from time to time as the situation may require.